1. Field of the Invention
The present invention relates to an image processing apparatus for, and method of, adding predetermined information to an input image and a storing medium which stores a program for implementing the method.
2. Related Background Art
Conventionally, as an output apparatus for performing a color print, a full-color printer, a full-color copying machine, a full-color facsimile apparatus or the like is practically used.
The output apparatus such as a color copying machine, a color printer or the like becomes cheaper every year and becomes more widely used.
On the other hand, quality of a printed image of the output apparatus has been improved. Therefore, it becomes possible to form an image having quality which is the same as that of an image of valuable securities or the like, whose image is generally prohibited from being reproduced. Consequently, there occurs concern that the image prohibited from being reproduced is illegally reproduced.
In order to inhibit such illegal image formation, conventionally, such a technique as putting predetermined additional information difficult to be perceived by human eyes on all images to be formed has been known. For example, in a case where a color image composed of yellow, magenta, cyan and black components is printed, a printing is to be performed by adding a dot pattern indicating the additional information to the yellow component. Consequently, the additional information can be extracted upon analyzing the yellow component and the dot pattern of a color image finally printed.
As the additional information, it is preferable to apply information which can easily grasp the image printed condition, for example, such information as a manufacturing number of copying machine, a manufacturer name or the like.
By the way, in a technique for adding additional information to an output image in order to detect a forgery action, even if the additional information is added by using a color which is the most difficult to be perceived, an extra signal should be added on an image signal. Accordingly, since the added signal acts as noise to an original image signal, there occurs such a problem as deteriorating quality of the output image. Especially, in a device which forms an image by performing binary image formation for each color such as an ink jet printer, that is, in a device for outputting an image on the basis of an image signal which is pseudo halftone processed depending on a dither method, an error diffusion method or the like, deterioration of image quality is generally found.
In a case where the additional information is added, the quality of the output image or detectability of the additional information is deteriorated in response to a characteristic of a recording medium. Therefore, in a case where the recording medium in a low level of a fixing characteristic of a toner is used, it is preferable to add the additional information under the condition of a high density or a large pattern size as long as possible in order to maintain the detectability of the additional information. In a case where the recording medium in a high transmittance is used, it is preferable to add the additional information under the condition of a low density or a small pattern size as long as possible in order to prevent the deterioration of image quality. That is, it is desirable to maintain a suitable balance between the quality of the output image and the detectability of the additional information in response to the characteristic of the recording medium.
However, in a conventional technique for adding additional information, a specific image processing means, which is different from a general image processing for adding the additional information, has to be provided. As a result, there has been a possibility of requiring a large cost for an apparatus and performing an image processing which is not adapted to another image processing such as a dither processing or the like.
The present invention is applied in consideration of the above-mentioned conventional example, and an object is to effectively add the additional information to an input image by utilizing the general image processing without executing the specific image processing.
More particularly, an object is to effectively add the additional information to the input image by utilizing N-value generation means for N-value generating a multi-value image.
To attain the above-mentioned object, according to a preferred embodiment of the present invention, an image processing apparatus of the present invention comprises input means for inputting M-value image data and N-value generation means for converting the M-value image data inputted by said input means into N-value image data, wherein the value M is larger than the value N, on the basis of threshold table groups composed of plural kinds of threshold tables whose using order is determined so as to indicate predetermined additional information.
The present invention maintains to attain the above-mentioned object, and still another object is to add the additional information depending on the most suitable forming pattern in accordance with the kind or characteristic of a recording medium.
To attain the above-mentioned object, according to a preferable embodiment of the present invention, the image processing apparatus of the present invention further comprises detection means for detecting the kind of recording medium on which an image indicated by the M-value image data inputted by said input means is to be formed, wherein the N-value generation means controls whether or not the N-value generation is performed to the M-value image data on the basis of the threshold table groups in accordance with the kind of the recording medium.
Other objects and features of the present invention will become apparent from the following embodiments and the attached drawings.